1. Field of the Invention
The present invention relates to a white organic electroluminescent device and a method of manufacturing the same, and more particularly, to a white organic electroluminescent device including a plurality of polymer light-emitting layers formed using a wet process, and a method of manufacturing the same.
2. Description of the Related Art
Organic electroluminescent (EL) devices are known for their high visibility due to their self-luminous characteristics, and for their superior anti-shock properties because they are made of solid state elements. So, utilizing the EL device as display devices has attracted considerable attention.
Organic EL devices basically include an anode, an organic light-emitting layer, a cathode, and optionally include a hole injection layer (HIL), a hole transport layer (HTL) or an electron injection layer (EIL). A typical organic EL device can have a structure including an anode, a HIL, a HTL, an organic light-emitting layer and a cathode, or can have another structure including an anode, a HIL, a HTL, an organic light-emitting layer, an EIL, and a cathode.
Recently, development of organic EL devices for display devices has been accelerated, in particular the development of a white organic electroluminescent device has been intensively accelerated. White organic EL devices are organic light-emitting devices which emit white light, and can be used as paper-thin light sources or backlights of liquid crystal displays (LCDs), or also can be used as full-color displays by adopting color filters.
A white organic EL device can include either a single light-emitting layer or a plurality of light-emitting layers. A white organic EL device with a single light-emitting layer can be manufactured either by using a single material or by doping or blending two or more materials in the light-emitting layer. One method uses a blue host, and red and green dopants. Another method uses a host material of large energy band gap, doped with red, green and blue dopants. However, energy transfer to dopants is incomplete in those methods. Also, another method that uses a bipolar host material, which has a red, green, or blue light emitting moiety, has a disadvantage that the adjustment of white balance is difficult.
White organic EL devices having a plurality of light-emitting layers can be classified into two types: a three-wavelength type and a two-wavelength type. The three-wavelength type white organic EL device includes stacked layers, which emits red (R), green (G), and blue (B) light, respectively. The two-wavelength type white organic EL device uses lights of complementary color. In the three-wavelength type white organic EL device, a method of manufacturing a plurality of light-emitting layers, which are made of materials of low molecular weight, has been tested, but in this method, it is difficult to control the diffusion of excitons and the thickness of each layer.
The two-wavelength type white organic EL device uses a combination of blue and yellow color, or bluish green and orange color, and the two-wavelength type white organic EL device has high efficiency compared to the RGB three-wavelength stacked layer type. However, there are still difficulties in controlling the diffusion of excitons and the thickness of each layer because of the materials of low molecular weight used in manufacturing the two-wavelength type white organic EL device. Therefore, a white organic EL device which improves the manufacturing process and maintains high efficiency of the organic EL device is required.